A potential role for BDNF in recognition behavior revealed through knockout in zebrafish

Brain-derived neurotrophic factor (BDNF) is a key player in the molecular mechanisms underlying learning and memory in mammals. Recent studies have shown that mutant fish lacking BDNF exhibit widespread deficits in learning tasks. Moreover, natural variation in brain BDNF gene expression predicts individual differences in learning ability in fish. These findings suggest that the role of BDNF in cognition may be widespread among vertebrates.

Following this hypothesis, we used a bdnf knockout zebrafish model to investigate whether BDNF is involved in recognition memory in fish. Zebrafish larvae were tested in a novel object recognition test, where their response to a previously encountered stimulus and a novel one was recorded.

Overall, zebrafish did not demonstrate a group-level preference for either stimulus. However, individuals appeared to show variation in their responses to the novel stimulus (either approaching or avoiding it). When accounting for the individual variation, the strength of recognition memory performance was lower in zebrafish lacking bdnf compared with control zebrafish, although this effect was influenced by the type of stimulus used. Moreover, the absence of BDNF resulted in less variability in the behavioral response towards the novel stimulus, supporting the role of this protein in shaping individual differences in behavior.

Our findings suggest that BDNF may be involved in recognition test performance and the underlying behavior, although the nature of this involvement and the contribution of memory processes remain unclear.